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Fortran (previously '''FORTRAN'''The names of earlier versions of the language through FORTRAN 77 were conventionally spelled in all-caps (FORTRAN 77 was the version in which the use of lowercase letters in keywords was strictly nonstandard). The capitalization has been dropped in referring to newer versions beginning with Fortran 90. The official language Standards now refer to the language as "Fortran." Because the capitalization (or lack thereof) of the word ''FORTRAN'' was never 100% consistent in actual usage, and because many hold impassioned beliefs on the issue, this article, rather than attempt to be normative, adopts the convention of using the all-caps ''FORTRAN'' in referring to versions of FORTRAN through FORTRAN 77 and the title-caps ''Fortran'' in referring to versions of Fortran from Fortran 90 onward. This convention is reflected in the capitalization of ''FORTRAN'' in the ANSI X3.9-1966 (FORTRAN 66) and ANSI X3.9-1978 (FORTRAN 77) standards and the title caps ''Fortran'' in the ANSI X3.198-1992 (Fortran 90) standard.) is a General-purpose Since FORTRAN 77, which introduced the CHARACTER data type., Procedural ,Since FORTRAN II (1958). Imperative Programming Language that is especially suited to Numeric Computation and Scientific Computing . Originally developed by IBM in the 1950s for scientific and engineering applications, Fortran came to dominate this area of programming early on and has been in continual use for over half a century in computationally intensive areas such as Climate Modeling , Computational Fluid Dynamics (CFD), Computational Physics , financial computing, and Computational Chemistry .Fortran (a Portmanteau derived from ''The IBM Mathematical Formula '''Tran'''slating System'') encompasses a lineage of versions, each of which evolved to add extensions to the language while retaining compatibility with previous versions. Successive versions have added support for processing of character-based data ( FORTRAN 77 ), Array Programming , Module-based Programming and Object-based Programming (Fortran 90 / 95 ), and Object-oriented and Generic Programming (Fortran 2003). HISTORY Mainframe (image courtesy of LLNL )]] , showing the specialized uses of columns 1-5, 6 and 73-80.]] In late 1953, John W. Backus submitted a proposal to his superiors at IBM to develop a more efficient alternative to assembly language for programming their IBM 704 mainframe computer. A draft specification for ''The IBM Mathematical Formula Translating System'' was completed by mid-1954. The first manual for FORTRAN appeared in October 1956, with the first FORTRAN Compiler delivered in April 1957. This was an Optimizing Compiler , because customers were reluctant to use a High-level Programming Language unless its compiler could generate code whose performance was comparable to that of hand-coded Assembly Language . While the community was skeptical that this new method could possibly out-perform hand-coding, it reduced the amount of programming statements necessary to operate a machine by a factor of 20, and quickly gained acceptance. Said creator John Backus during a 1979 interview with Think, the IBM employee magazine, "Much of my work has come from being lazy. I didn't like writing programs, and so, when I was working on the IBM 701 (an early computer), writing programs for computing missile trajectories, I started work on a programming system to make it easier to write programs," http://www.msnbc.msn.com/id/17704662/ The language was widely adopted by scientists for writing numerically intensive programs, which encouraged compiler writers to produce compilers that could generate faster and more efficient code. The inclusion of a Complex Number Data Type in the language made Fortran especially suited to technical applications such as electrical engineering. By 1960, versions of FORTRAN were available for the IBM 709 , 650 , 1620 , and 7090 computers. Significantly, the increasing popularity of FORTRAN spurred competing computer manufacturers to provide FORTRAN compilers for their machines, so that by 1963 over 40 FORTRAN compilers existed. For these reasons, FORTRAN is considered to be the first widely used programming language supported across a variety of computer architectures. The development of FORTRAN paralleled the early evolution of compiler technology; indeed many advances in the theory and design of Compiler s were specifically motivated by the need to generate efficient code for FORTRAN programs. FORTRAN The initial release of FORTRAN for the IBM 704 contained 32 statements, including:
Below is a part of the 1957 paper, "The FORTRAN Automatic Coding System" by Backus, et al., with this snippet on the FREQUENCY statement and its use in a compile-time Monte Carlo Simulation of the run-time to optimise the code generated. Quoting ...
FORTRAN II IBM's ''FORTRAN II'' appeared in 1958. The main enhancement was to support Procedural Programming by allowing user-written subroutines and functions. Six new statements were introduced:
Over the next few years, FORTRAN II would also add support for the DOUBLE PRECISION and COMPLEX data types.FORTRAN III operators. Now obsolete.]] IBM also developed a ''FORTRAN III'' in 1958 that allowed for inline assembler code among other features; however, this version was never released as a product. Like the 704 FORTRAN and FORTRAN II, FORTRAN III included machine-dependent features that made code written in it unportable from machine to machine. Early versions of FORTRAN provided by other vendors suffered from the same disadvantage. FORTRAN IV Starting in 1961 , as a result of customer demands, IBM began development of a ''FORTRAN IV'' that removed the machine-dependent features of FORTRAN II (such as READ INPUT TAPE), while adding new features such as a LOGICAL data type, logical Boolean Expression s and the ''logical IF statement'' as an alternative to the ''arithmetic IF statement.'' FORTRAN IV was eventually released in 1962, first for the IBM 7030 ("Stretch") computer, followed by versions for the IBM 7090 and IBM 7094 .FORTRAN 66 Perhaps the most significant development in the early history of FORTRAN was the decision by the ''American Standards Association'' (now ANSI ) to form a committee to develop an "American Standard Fortran." The resulting two standards, approved in March 1966, defined two languages, ''FORTRAN'' (based on FORTRAN IV, which had served as a ''de facto'' standard), and ''Basic FORTRAN'' (based on FORTRAN II, but stripped of its machine-dependent features). The FORTRAN defined by the first standard became known as ''FORTRAN 66'' (although many continued to refer to it as FORTRAN IV, the language upon which the standard was largely based). FORTRAN 66 effectively became the first "industry-standard" version of FORTRAN. FORTRAN 66 included:
FORTRAN 77 After the release of the FORTRAN 66 standard, compiler vendors introduced a number of extensions to "Standard Fortran", prompting ANSI in 1969 to begin work on revising the 1966 standard. Final drafts of this revised standard circulated in 1977, leading to formal approval of the new FORTRAN standard in April 1978. The new standard, known as ''FORTRAN 77'', added a number of significant features to address many of the shortcomings of FORTRAN 66:
: (ASCII functions were demanded by the U. S. Department Of Defense , in their conditional approval vote.) In this revision of the standard, a number of features were removed or altered in a manner that might invalidate previously-standard-conforming programs. (Removal was the only allowable alternative to X3J3 at that time, since the concept of "deprecation" was not yet available for ANSI standards.) While most of the 24 items in the conflict list (See Appendix A2 of X3.9-1978) addressed loopholes or pathological cases permitted by the previous standard but rarely used, a small number of specific capabilities were deliberately removed, such as:
:: GREET = 12HHELLO THERE!
:: DIMENSION A(10,5)
:: Y= A(11,1)
An important practical extension to FORTRAN 77 was the release of MIL-STD-1753 in 1978. This specification, developed by the U. S. Department Of Defense , standardized a number of features implemented by most FORTRAN 77 compilers but not included in the ANSI FORTRAN 77 standard. These features would eventually be incorporated into the Fortran 90 standard.
The IEEE 1003.9 POSIX Standard, released in 1991, provided a simple means for Fortran-77 programmers to issue POSIX system calls. Over 100 calls were defined in the document - allowing access to POSIX-compatible process control, signal handling, file system control, device control, procedure pointing, and stream I/O in a portable manner. The development of a revised standard to succeed FORTRAN 77 would be repeatedly delayed as the standardization process struggled to keep up with rapid changes in computing and programming practice. In the meantime, as the "Standard FORTRAN" for nearly fifteen years, FORTRAN 77 would become the historically most important dialect. Fortran 90 The much delayed successor to FORTRAN 77, informally known as ''Fortran 90'', was finally released as an ANSI Standard in 1992. This major revision added many new features to reflect the significant changes in programming practice that had evolved since the 1978 standard:
=Obsolescence & Deletions Unlike the previous revision, Fortran 90 did not delete any features. (Appendix B.1 says, "The list of deleted features in this standard is empty.") Any standard-conforming FORTRAN 77 program is also standard-conforming under Fortran 90, and either standard should be usable to define its behavior. A small set of features were identified as "obsolescent" and expected to be removed in a future standard. Fortran 95 ''Fortran 95'' was a minor revision, mostly to resolve some outstanding issues from the Fortran 90 standard. Nevertheless, Fortran 95 also added a number of extensions, notably from the High Performance Fortran specification:
An important supplement to Fortran 95 was the age. In addition, Aliasing is not an issue for optimization of array references, allowing compilers to generate faster code than in the case of pointers.) Another important supplement to Fortran 95 was the and Floating Point Exception Handling . Conditional Compilation and Varying length strings In addition to the mandatory "Base language" (defined in ISO/IEC 1539-1 : 1997), the Fortran 95 language also includes two optional modules:
which, together, comprise the multi-part International Standard (ISO/IEC 1539). According to the standards developers, "the optional parts describe self-contained features which have been requested by a substantial body of users and/or implementors, but which are not deemed to be of sufficient generality for them to be required in all standard-conforming Fortran compilers." Nevertheless, if a standard-conforming Fortran does provide such options, then they "must be provided in accordance with the description of those facilities in the appropriate Part of the Standard." Fortran 2003 The most recent standard, ''Fortran 2003'', is a major revision introducing many new features. A comprehensive summary of the new features of Fortran 2003 is available at the ISO Fortran Working Group (WG5) official Web site, and may be downloaded directly as a or gzipped PostScript file .From that article, the major enhancements for this revision include:
Fortran 2008 Efforts are underway to develop a revision to Fortran 2003, tentatively called Fortran 2008. As with Fortran 95, this is intended to be a minor upgrade, incorporating clarifications and corrections to Fortran 2003, as well as introducing a select few new capabilities. Proposed new capabilities include
A full list is in the report "The language features that have been chosen for Fortran 2008" . The legacy of FORTRAN Since Fortran has been in use for nearly fifty years, there is a vast body of Fortran in daily use throughout the scientific and engineering communities. It is the primary language for some of the most intensive supercomputing tasks, such as CPU2000 benchmarks), an eloquent tribute to the longstanding excellent floating-point performance of the language. LANGUAGE FEATURES The ''Fortran language features'' described are intended to be a fairly comprehensive overview of the Fortran language; full details may be found in any of several Fortran textbooks. Only those features widely used in new programs are described, as few of the historic features are used in modern programs. Still, most have been retained in the language to maintain Backward Compatibility . PORTABILITY Portability was a problem in the early days because there was no agreed standard—not even IBM's reference manual—and computer companies vied to differentiate their offerings from others by providing incompatible features. Standards have improved portability. The 1966 standard provided a reference syntax and semantics, but vendors continued to provide incompatible extensions. Although careful programmers were coming to realize that use of incompatible extensions caused expensive portability problems, and were therefore using programs such as ''The PFORT Verifier,'' it was not until after the 1977 standard, when the National Bureau of Standards (now NIST ) published ''FIPS PUB 69'', that processors purchased by the U.S. Government were required to diagnose extensions of the standard. Rather than offer two processors, essentially every compiler eventually had at least an option to diagnose extensions. Incompatible extensions were not the only portability problem. For numerical calculations, it is important to take account of the characteristics of the arithmetic. This was addressed by Fox et al. in the context of the 1966 standard by the ''PORT'' library. The ideas therein became widely used, and were eventually incorporated into the 1990 standard by way of intrinsic inquiry functions. The widespread (now almost universal) adoption of the IEEE 754 standard for binary floating-point arithmetic has essentially removed this problem. Access to the computing environment (e.g. the program's command line, environment variables, textual explanation of error conditions) remained a problem until it was addressed by the 2003 standard. Large collections of "library" software that could be described as being loosely-related to engineering and scientific calculations, such as graphics libraries, have been written in C, and therefore access to them presented a portability problem. This has been addressed by incorporation of C interoperability into the 2003 standard. It is now possible (and relatively easy) to write an entirely portable program in Fortran, even without recourse to a preprocessor. VARIANTS OF FORTRAN Specific variants Vendors of high-performance scientific computers (''e.g.,'' Burroughs , CDC , Cray , Honeywell , IBM , Texas Instruments , and UNIVAC ) added extensions to Fortran to take advantage of special hardware features such as Instruction Cache , CPU Pipelines , and vector arrays. For example, one of IBM's FORTRAN compilers (''H Extended IUP'') had a level of optimization which reordered the Machine Language Instructions to keep multiple internal arithmetic units busy simultaneously. Another example is ''CFD'', a special variant of Fortran designed specifically for the ILLIAC IV supercomputer, running at NASA 's Ames Research Center . Object-Oriented Fortran was an object-oriented extension of Fortran, in which data items can be grouped into objects, which can be instantiated and executed in parallel. It was available for Sun, Iris, iPSC, and nCUBE, but is no longer supported. Such machine-specific extensions have either disappeared over time or have had elements incorporated into the main standards; the major remaining extension is OpenMP , which is a cross-platform extension for shared memory programming. One new extension, CoArray Fortran , is intended to support parallel programming. Fortran-based languages Prior to FORTRAN 77, a number of Preprocessor s were commonly used to provide a friendlier language, with the advantage that the preprocessed code could be compiled on any machine with a standard FORTRAN compiler. Popular preprocessors included FLECS , MORTRAN , Ratfor , and Ratfiv . (Ratfor and Ratfiv, for example, implemented a remarkably C -like language, outputting preprocessed code in standard FORTRAN 66.This is not altogether surprising, as Brian Kernighan , one of the co-creators of Ratfor, is also co-author of ''The C Programming Language''. ) The Fortran-95 Standard includes an optional ''Part 3'' which defines an optional Conditional Compilation capability. This capability is often referred to as "CoCo". Many Fortran compilers have integrated subsets of the C Preprocessor into their systems. SIMSCRIPT is an application specific Fortran preprocessor for modeling and simulating large discrete systems. F was designed to be a clean subset of Fortran 95 that attempted to remove the redundant, unstructured, and deprecated features of Fortran, such as the EQUIVALENCE statement.CODE EXAMPLES The sample programs can be compiled and run with any standard Fortran compiler (see the End Of This Article for lists of compilers). Most modern Fortran compilers expect a file with a .f or .for extension (for FORTRAN 66 or FORTRAN 77 fixed-form source, although the FORTRAN 66 dialect may have to be selected specifically with a command-line option) or .f90/.f95 extension (for Fortran 90/95 free-form source, respectively).FORTRAN QUOTATIONS For a programming language with a half-century legacy, FORTRAN not surprisingly has accumulated its share of jokes and folklore. From the historical record
References in popular culture
FORTRAN ANECDOTES FORTRAN II on the IBM 1401 and 1460 The IBM 1401 computer, introduced in 1959, supported Fortran by the middle 1960s although the 1401 was intended for decimal business computation and as a primitive printer "server" that would print the contents of magnetic tapes, prepared on much larger systems such as the IBM 7090. The absolute minimum configuration was supported, for example, at Roosevelt University in Chicago until 1974 (cf. Edward G. Nilges, "Build Your Own .Net Language and Compiler", Apress 2004). This configuration was 8K of 6-bit bytes for RAM and a card reader and punch (cf. Nilges, "Anecdotes", IEEE Transactions on the History of Software, Spring/Summer 1999). The compiler, as described below, was a series of about 100 small overlay phases (cf. John A. N. Lee, "The Anatomy of a Compiler", Van Nostrand Rheinhold 1968), where a miniature monitor stayed resident in memory to load each phase. These phases were loaded from a card deck of more than 2,000 punched cards (more than two feet long) or from a tape drive (which wasn't available at the Roosevelt University installation). These overlays would scan and parse a "squozed" (blank-removed: run length encoded) form of the source code to produce statements in an interpretive language at the end of available memory (since the end of memory could not be sensed, it had to be spelled out on a "control card"). The final phase was responsible for interpreting the code. Despite the primitive Fortran II compiled, which had no strings, the rather complex and flexible FORMAT statement was supported. In addition, another "control" card could specify how many decimals would be supported in floating point format; this feature looked forward to a vastly more flexible feature in today's Mathematica system. However, for a number of years, the installation at Roosevelt University was deprived of Fortran despite the availability of the compiler "deck". At some point in time in 1970, an IBM customer engineer had "fixed" a bug, thought to result from the absence of special-purpose multiply/divide hardware (for which 1401 customers had to pay extra) by overlaying memory with a jump to a subroutine for multiplication and division. Unfortunately, on the minimal configuration, this destroyed instructions and never worked for this reason. Roosevelt was paying for multiply and divide, so, when in 1972 the customer engineer's patch was removed, the compiler then worked. It was used for administration, teaching and research until about 1977. The IBM 1460 (similar to the 1401) also had a Fortran II compiler that resided on tape. It required only that Tape Drive , a Card Reader/punch and a Printer , i.e. no "work" devices. The compiler for the 1401 and 1460 was in the form of a multitude of tiny phases, or segments, that were passed over the source program which was held in storage throughout the compile. The first phase read the program from the card reader, numbered the statements, and produced a source listing. The next phases might be something like "copy (and reverse) the program from low storage to high storage, assigning and replacing the names with Tokens ." The appearance was that the system tape containing the compiler would "blip", the computer would hum for a bit, then the tape would "blip" again and another part of the listing would appear on the printer. The end result was an object deck on the punch, and the program was left in storage and ready to go. The effect was quite unusual, and was designed to be able to compile the largest possible program with the fewest Peripheral devices. Letter O considered harmful During the same Fortran Standards Committee meeting at which the name "FORTRAN 77" was chosen, a technical proposal was somehow smuggled into the official distribution, bearing the title, "Letter O considered harmful". This deceptively simple proposal purported to address the confusion that sometimes arises between the letter "O" and the numeral zero, by eliminating the letter from allowable variable names. However, the method proposed was to eliminate the letter from the character set entirely (thereby retaining 48 as the number of lexical characters, which the colon had increased to 49). Among the "PRO" arguments was the assertion that this would also promote structured programming, by making it impossible to write a GO TO statement. (Troublesome FORMAT statements would be eliminated, as well.)The sole "CON" argument conceded that "this might invalidate some existing programs" but noted that most of these "probably were non-conforming, anyway". 23:44, 30 August 2007 (UTC) REFERENCES Textbooks "Core" language standards Related standards NOTES EXTERNAL LINKS History
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